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What is the purpose of blades on a compressor?
What is the point of having blades on a compressor. I heard on NASA that it alters the flow but how would this help. As the flow of a fluid increases, the pressure decreases, and vice versa. The rotors increase the speed of the air and descreases the pressure and the stators decrease the speed of the air and increase the pressure. How would this help create higher pressure. Why not just have the rotors? I know that the ducts this whole thing goes in gets smaller as it goes on, does this play a role? Don't get all complicated here on me, I'm still learning about airplanes and flying. Try to be as simple as possible, thank you.

By blades, do you mean stator vanes?

@Sanchises I mean ths rotor and the stator

There is such a thing as a ramjet, which does not require compressor blades, but you have to be flying fast to make it work at all and it is not practical for most kinds of aircraft.

The statement about the rotor blades ("the rotors increase the speed of the air and descrease the pressure") is not correct, because Bernoulli's Equation does not apply in this situation. Hence, the statement "as the flow of a fluid increases, the pressure decreases, and vice versa" isn't appropriate for the rotating compresser blades.
Bernouilli's equation (below) assumes no energy is being added or removed from the fluid. This is true when the fluid is flowing through the stationary stator vanes, but not the rotating blades.
The rotating blades increase the velocity, but do not decrease the static pressure, becuase they are adding mechanical work (energy) to the fluid. This energy (or power) comes from the turbine.
When no energy is being added to the fluid:
$$
total\space pressure = static\space pressure + 1/2 \rho v^2
$$
where
$\rho$ is the density and $v$ is the velocity.
This is the mathematical equivalent of your statement "as the flow of the fluid increase, the static pressure decreases".
But, the rotating blades add total energy. So this equation does not apply, so as the velocity increases, static pressure does not go down. But, total energy has increased, by the mechanical work done by the blades. So the value on the left of the equation goes up as the fluid flows through the rotating blades. Next, the fluid flows through the stationary stator vanes. Because they are static, they add no energy, so Bernoulli's equation now does apply. Hence, as the velocity is decreased, the static pressure goes up (i.e. there is no change in total pressure).
If you just have the rotor blades, and no stator vanes, the compressor would just make the fluid move (i.e an increase in the total pressure) but with no increase in static pressure. The stator vanes slow the fluid down, and convert the velocity into an increase in static pressure.
You need to understand the difference between total and static pressures.

so the air moves past the rotation blades and the total pressure is increased beucase it's adding mechanical work  (energy). Does this mehcinal work also make the air flow? Then when it passes by the stator blades it increases the static pressure, correct?

@Itzyoboi. Your comments are correct. Adding mechanical work to the fluid is necessary to make it flow, but is not the only thing necessary. If you replaced the blades with rods for example, energy would still be added to the fluid, but it would just be stirred up. The aerofoil shape of the blades is also crucial. And if you just had aerofoil shaped blades, and they did not move, the air will not flow either. You need both.

ok makes perfect sense, thank you. Now my only question is why would you need an increase in static pressure? And does the energy that the air have also heat it, or does the velocity that it has heat it?

@Itzyoboi.  Combusting the fuel at high pressure improves the combustion efficiency. See figure 1 here:https://en.m.wikipedia.org/wiki/Brayton_cycle The velocity in the combustor can't be too high, or the flame gets blown out (crudely speaking). Typically the velocity is lower than the aircraft speed, so the flow is decelerated. Compressing the air cause its temperature to rise. An inefficient compressor also causes it to rise a bit more than it theoretically should.

@Itzyoboi.  Sorry, combustion at high pressure improves the overall efficiency of a gas turbine. I can't edit my comment above.

doesn't total energy have high pressure to, or do the rotor blades make high energy and energy is velocity and the stator blades convert the energy into pressure. So the rotor blades don't create pressure they create energy right?

@Itzyoboi.  You might want to read https://en.m.wikipedia.org/wiki/Axial_compressor and https://www.grc.nasa.gov/www/k-12/airplane/caxial.html. If you just had rotor, rotor, rotor, etc and a single stator at the end, the flow would end up swirling/ spiralling, and there would be no  difference in the (radial) velocity of the blades and the air. i.e. the air would just be circulating at the same RPM of the blades and they would have no benefit.

Isn't the RPM of the blades high though? And do the rotors increase the energy or pressure beucase this would make sense if the rotor blades increase the energy and the stator blades slow the fuild and increase the pressure. And the whole channel that the compressors is in gets smaller and smaller, does this help increases pressure? Doesn't the static pressure stay in the section of the stator vane? And do you learn about this stiff in high school physics or colloege physics?

@Itzoboi.  Too many questions too answer in this space with no diagrams or equations. Suggest you look for info on "axial compressor aerodynamics", or performance. The static pressure does not stay in the stator section. Bernoulli's equation is a first year university or college  topic. Gas turbine compressor blade aerodynamics is not usually covered in a degree, but more likely learnt in a job, or post graduate study.

Ok, so how do you know so much? And the last question I would like to be answered is do the rotor blades increase total energy or total pressure?

@Itzyoboi.  My info comes from almost 30 years in the industry. I don't see a difference between total pressure and total energy. But to keep it simple, let's say the rotor blades increase total pressure, as written in Bernoulli's equation above. Cheers.

Thank you a lot, even though not all of my question were answered a lot were, do you think if I ask my high school physics teacher she will know the answers to my questions?

@Itzyoboi. I'd expect she would know Bernoulli's equation. I wouldn't expect she'd know about the aerodynamics of gas turbine compressor, however.

You're talking about an engine. Bernouilli is valid for free flow when no energy is added to the airflow, and adding energy to the airflow is exactly what a jet engine does. Inside an engine, it is perfectly possible to increase both pressure and speed. It is not done that way because higher pressure is what is required, but it is possible.
This energy added to the airflow is applied by the rotors, in the same way that a propeller does. In doing so, they also make the airflow swirl around a bit, and the stators twist the flow back. That is all they do, make life easier for the next rotor stage to do their work. Stators don't impart any energy on the flow.

Do the stators take away energy? Does the energy that is added to air, does it increase the pressure?

@Itzyoboi Only friction energy, a tiny bit. The energy added to air means that total pressure rises, which can be distributed to dynamic pressure or static pressure or both. The main function of the compressor is to increase the static pressure, so the increase in total pressure added by the rotor will be channeled into static pressure as much as possible.

thank you, you make sense. And the energy also adds heat correct? Or does the velocity add heat?

All energy added is partly transformed into heat. Temperature follows similar lines to pressure: total temperature stays constant if no energy is added, and can be transformed into either internal energy or kinetic energy or both: at a specific total temperature, static temperature rises when velocity lowers and vice versa.

so it gets hotter in the section of the stator blades? And why do you need an increase in static pressure instead of total pressure? Why do compressors want static pressure?

No the stator blades don't add anergy and don't change the linear velocity, they are only there to twist the flow back. For good combustion conditions, you want to raise static pressure and limit stream velocity. Startic pressure can later be traded in for kinetic energy to drive the turbine.

so total energy can't be traded in for kentietc energy to drive the turbine? Why don't you want high flow velocity? And why not just have a bunch of rotor blades and then one stator blade at the end to collect all the total pressure that has built up and change it into static pressure? Why have one rotor blade then one stator blade? Doesn't the static pressure stay in the section of the stator blade? Sorry for so many question if there is a website,video, or book you know if that can explain all my question then you can tell me about that

In simple terms, the compressor blades (both the fixed stator blades and the rotating "fan" blades) in the front of the engine are an air pump: the rotating blades actively draw air into the engine and squeeze it, raising its pressure. the work required to compress the air is large, and comes from the power-extraction turbine at the back end of the engine. Many rotor/stator pairs are present in the compressor side of the engine; each one squeezes the air further and further, raising its pressure further and further. At the end of the process, the air exits the compressor and is sent on to the combustors.


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Is there a specific formula or way to calculate flex temperature for an Airbus A320?
I have hear of RTOW charts but I haven't seen any calculations with the runway length or slope. What is the formula or equation to finding flex temperature and V-Speeds?

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Did Airbus bring back LAF (Load Alleviation Function) on A320s with Sharklets?
I have heard that the A320 no longer has LAF (Load Alleviation Function) except for really old ones, but I also heard that A320s with Sharkelts do have LAF. So is it true that Airbus got rid of LAF on A320s and implemented it back on A320s with Sharklets, if so does anybody know why, because I heard Airbus says they go rid of it because it was not needed, so why would they add it back if they did? I heard it has something to do with that it increases MTOW (Maxium Takeoff Wight).

What are Sharklets?  Had to find a source - looks like curvier winglets than that is normally seen on jets.

https://en.wikipedia.org/wiki/Wingtip_device#/media/File:Lufthansa_winglet_(14511808755).jpg

@CrossRoads you've got your answer by the looks of it, but for the record, they were also known as blended winglets on the 73NG.

LAF is a function that alleviates load on wings roots, but was causing early wear to the actuators and to ailerons and spoilers hinges.
No LAF is not available on latest A320’s

Do you have a source for that?

LAF is installed on the latest skarklets, do you have any source for your info?

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Does the PFD/ND XFR work when the PFD is on the ND screen on the Airbus A320?
So I know the PFD has priority over the ND and that's why if the PFD screen fails its automatically switched to the ND screen. If the ND screens fails it does not get automatically transferred to the PFD screen because the PFD has priority. You can view the ND screen on the PFD screen by pressing the PFD/ND XFR button. So my question is if the PFD is on the ND screen because the PFD screen failed if you press the PFD/ND XFR will it show the ND information on the ND screen, and when you press it again it will go back to the PFD?

From the FCOM A320:

As you can see if you fail the PFDU and the PFD is transferred on the NDU, by pressing XFR PFD/ND you will have the ND appearing on the NDU
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A couple of questions about Aeroflot flight 593
I recently heard about Aeroflot flight 593 and I know the cause is pilot error or whatever you would like to call that, but I have a couple of question about the aircraft.

First of all, I have never heard of part of the autopilot disconnecting. I have never heard of just the ailerons of the autopilot disconnecting, was this just a feature of the aircraft? Can any new Airbus or any modern day aircraft's autopilot partly disconnect to a system?
Lastly I know the autopilot pitched up and increased thrust to gain altitude but why did it stall, why didn't the autopilot stop pitching the nose up and increasing thrust once it got to high and dangerous?

The autopilot will disengage if the controls are manually manipulated while the autopilot is on.  The main issue with this particular airplane was that there was no audible autopilot enunciation that indicated that the autopilot turned off which is what the pilots were used to hearing on Russian made jets.  Rather there was only an indication light that would go on if autopilot disengaged and could go unnoticed.  The autopilot disengagement was not noticed right away and the aircraft entered into a spiral spin.  The pilots tried to recover from the spin but they pulled up too much (over corrected) and the plane entered a stall.
Autopilots can disengaged automatically for a number of reasons.  For example Air France 447 autopilot disengaged due to conflicting information from the airspeed indicators.  Incorrect actions by the pilots after the autopilot disengagement caused that accident.  In modern day aircraft the autopilot disengagement is heard as an audible signal so the pilot knows to take over.  If Aeroflot 593 had this feature the accident could have been avoided (besides not having your kids fly the airplane).
To answer your questions about he various levels of autopilots there is really only one autopilot that works in conjunction with other automated systems to fly the plane below is a description of the various systems:
Autopilot:  Automatically flies the plane according to instruments.  This system is responsible for manipulating the control column.
Auto-Thrust:  Automatically adjust thrust to maintain a constant airspeed.
Yaw-Dampening: Automatically adjust rudders for coordinated turns.  Yaw-Dampening can work when autopilot is on or when the airplane is manually flown.
Just because the autopilot disengages does not necessarily mean the other systems disengage.

ok that makes sense, but what about the autopilot over pitching and for the thrust to increases once it reaches an unsafe level?

The autopilot did not over pitch it was disengaged.  The pilot over pitched which caused the stall.  Also from the CVR transcript is looks like the pilot ordered more thrust and wasn't controlled by the auto-thrust.  All the "autopilot" systems should disengaged when the aircraft enters an unusual attitude.

You may be confusing autopilot with the flight protections of fly-by-wire aircraft.  Fly-by-wire was not introduced until the A320 so no fly-by-wire protections were on this aircraft.

I thinks so too, thanks for all your help :)

so in the wikipedia site it says "The autopilot (which no longer controls the ailerons) used it's other controls in a bid to compensate, pitching the nose up, and increasing thrust. The plane begins go stall. The autopilot, unable to cope, disengages completely." So why didn't the autopilot stop once it got to a too high attitude? Would fly-by-wire system, which you said isn't on that plane have not allowed it to get to that attitude and it only got to that high of an attitude beucase it didn't have a fly-by-wire system?

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Does the speed of the air molecules matter in aircraft performance?
Does the fact that air molecules move slower in cold weather and faster in hot weather also affect the aircraft's performance or no? So if its cold there is a higher chance or air molecules hitting the wing and engines because the air molecules are compacted and slow moving and in hot weather they are spread out and faster moving, so less of a chance of air molecules hitting the wings and going into the engine. So in cold weather the molecules move slow and in hot weather they move faster, does this also effect aircraft performance. I know that the fact that in cold air the air is more compacted and that increases aircraft performance but does the fact that it moves slow also have an effect on aircraft performance? Same with hot air, the air is more spread out which reduces aircraft performance but does the fact that the air molecules are moving fast have an effect on aircraft performance?

In some sense, yes it does.  But we usually don't think about it in those terms.  You usually only need to think about individual air molecules when the object you are talking about is very small.  For example, if you are trying determine the aerodynamics of an airplane whose length is 1/100th diameter of a human hair, then you might start caring about individual air molecules. For realistic sized planes, the planes are so big relative to the air molecules that we can just pretend that air is continuous. So instead of thinking about the motion of individual air molecules, we think about continuous variables such as density and temperature.  i.e. when your air molecules "spread out and faster moving" we say that is a higher temperature with a corresponding lower density, and when they are "compacted and slow moving" we say that is lower temperature and a higher density.  By doing that, we've taken the motion of a quadrillion individual air molecules and reduced it down to one single number. And that one single number, density, does have an affect on aircraft performance.
For completeness, you also sometimes need to consider individual air molecules at very low pressures.  e.g. if your air pressure is a millionth of an atmosphere, then there are not many air molecules to go around and so each individual molecule's motion becomes more significant.  But airplanes generally do not fly at such low pressures.  Even at 40,000 ft, there's a lot more air pressure than that.

Nice, thick cold air is great for engine performance. Especially for small single engine airplanes.
Hot, less dense air means less performance, making takeoff more of a problem, with longer takeoff rolls needed to get sufficient airspeed to liftoff.

Yes, of course, but not because of the average speed of the molecules.
Temperature affects density altitude.
Aircraft performance is dependent on density altitude, which considers not only the pressure altitude, (displayed on your altimeter), but air temperature as well. Almost every performance metric for an aircraft is a function of density altitude, which increases as temperature increases, and decreases when it is colder. Lift, drag, engine performance, all are affected by density altitude.
The fact that the air molecules are moving faster when it is hotter is irrelevant, because this speed is the average speed of the molecules. they are moving in all directions, both towards the airfoil, and away from it. So any performance increase from additional relative speed of those air molecules moving towards the wing will be counterbalanced by the performance decrease from those air molecules moving in the same direction as the aircraft, which will be hitting the wing at an equivalently slower speed.


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What is this crashed WW2 era aircraft?
There is a post D-Day Nazi propaganda film (with contemporary Allied narration) available on YouTube. It shows a destroyed aircraft at 11:50, presumably Allied.
It looks like a twin-engine aircraft, although there may be a buckled propeller in front of the cockpit.

source

It looks like a four engine bomber lying on its back. The air intakes on the leading edge leads me to believe it is a B-17.
I have inverted a couple of B-17 photos for reference:

Yes it's absolutely a B-17. Nice work!  I didn't know B17s had inverted flight capability!  Oh wait...

Ah yes, what I thought was the cockpit is a wheel. Good work!

@JohnK Every plane can fly inverted once...

You can fly any airplane inverted if you want, just not with the engines running in most cases.

“I didn't know B17s had inverted flight capability!” This plane isn’t flying; it has crashed.

@JohnK It depends on the carburetor. At least some versions of the Spitfire had a float carburetor that resulted in the engine cutting out if flying inverted.

@Davidw Also depends on the fuel system. Many aircraft that weren't designed for inverted flight have gravity-fed fuel systems. Those don't work well in inverted flight.

Could you shut the engines off at a high enough airspeed, fly inverted for a bit, turn back upright, and get them restarted? Or would the airframe not even survive the two half-rolls?

@Sixtyfive Two things: inverted doesn't necessarily mean negative G-force. Only the latter would be a problem for certain systems if sustained to long. The engines would simply restart by themselves once the get fed fuel again after a neg G cut out. And the other one: the airframe has to survive random turbulence - those cause higher stress then a well controlled half-roll. (Also consider the safety margins the anticipated random holes demand!)

In the southern emisphere sky and sea are inverted..problem solved

@Sixtyfive https://youtu.be/3IV9PZW1N9U  The quality of the digitization isn't that great, but if a 707 can do it...


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Did Hamilton Sundstrand Corporation fix this GPWS problem?
So I was reading about Garuda Indonesia Flight 152 and one of the reason it crashed was for a GPWS malfunction. Here is the Wikipedia article about the crash and GPWS: Garuda Indonesia Flight 152

The plaintiffs alleged that the GPWS was defectively designed, that the manufacturer was aware of its deficiencies in mountainous terrain for over a decade, and had the system worked as designed the accident could have been avoided.

Was this problem ever fixed? Did Hamilton Sundstrand Corporation fix the problem? Also I was wondering if anybody knows what company makes the GPWS for an Airbus A350 and an Airbus A320?

GPWS is considered obsolete and was phased out in the early 2000s.

Despite what the Wikipedia article states, Hamilton Sundstrand did not make the GPWS.  Sundstrand Data Control built the GPWS. Sundstrand Data Control was purchased by AlliedSignal in 1993 from Sundstrand Corporation.  AlliedSignal later purchased Honeywell International in 1999, taking the Honeywell name.  Honeywell is the current owner of the GPWS/EGPWS product line.  Sundstrand Corporation was purchased by UTC in 1999 and merged with Hamilton Standard to become Hamilton Sundstrand under UTC.

@user71659: GWPS itself is not obsolete.  The earlier forms of GPWS are obsolete - EGPWS/TAWS is still a form of GPWS.

EGPWS/TAWS is the fix for this problem...
The original Ground Proximity Warning Systems were indeed quite limited due to their inability to know anything about anything besides what was under the plane at the time.  While one could theoretically use ground-mapping radar techniques similar to military terrain following radar for this, that would be dancing in a minefield of classification and relatively advanced signal processing, making it impractical for use in the civil aviation environment.
Instead, EGPWS (enhanced ground proximity warning system)/TAWS uses the aircraft's idea of its own position (from the onboard navigation systems) along with a database of terrain info to generate forward looking warnings in addition to the more straightforward radio-altimeter warnings generated by GPWS.  This is what is found on basically all aircraft in mainline airline service these days, as well as many more modern business jets and commuter-type aircraft as well.
but even TAWS won't save you if you're getting lied to about where you are!
Nonetheless, it's still possible to have a non-pilot-error CFIT in an EGPWS/TAWS equipped aircraft -- on one fateful day in Ethiopia, a British Mediterranean Airlines A320 nearly became a crater twice over thanks to the ADS VOR/DME providing bad bearing information to anyone who tried to use it as a navaid -- without GPS, the only thing the TAWS had to go on was the VOR-updated IRU position, which was being thrown off by the bad data from the ADS VOR.  Luckily for the passengers, the crew had their wits about them and caught the situation before smashing into the ground, but even with GPS being nearly universal in airliners compared to its prevalence in 2003, interference, spoofing, or jamming of GPS signals is still a threat, as this year's Red Flag exercises are reminding us quite vividly by taking out GPS service across much of the western CONUS.


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Does any one know if the PFD or ND or any other screen on an commercial aircraft work like a computer or something else?
Does any one know if the PFD or ND or any other screen on an commercial aircraft work like a computer or something else? Like does the screen work like a computer and read 0s and 1s like maybe for sensors for smoke it sends a particular amount of 0s and 1s to show on the screen there is a fire and have hard drives and graphic cards and all that stuff or do they work completely different?

They are essentially standard computers.  They frequently run a custom OS, but run on fairly mainstream processors, and are programmed with typical low-level programming languages.

All multi-functional displays in modern avionics are just computers. Typically, they are only responsible for presentation of the supplied information, but may do some processing: for example, display certain alerts in the right conditions. Also, they manage some of the user pilot input and mode switching.

G1000 PFD diagnostics page
Nearly all the data comes in on digital bus(es), in aviation most commonly ARINC 429 or even Ethernet with a custom protocol.
Bare sensors either have a dedicated microcontroller that converts the readings to a digital format, or are connected to a dedicated processing unit (also a specialised computer), such as ADC (Air Data Computer) which collects and processes all the air-related data (airspeed, altitude, temperature, etc.)
Even then, typically, this semi-processed data don't go to displays directly. All the sensor data are collected by a sort of integration unit (e.g. GIA for Garmin systems), which does most of the processing and decision making. Then, the necessary information is relayed to the displays.

Zeus so the Airbus ECAM system would be equivalent to what you said?

@GaryZenger, I'm not intimately familiar with it, but basically yes; my understanding is that ECAM is conceptually equivalent to GIA that I mentioned.


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Is it realistic for a WW2 aircraft to dive to extinguish an engine fire?
In the film "Memphis Belle" there is a scene in which the titular plane is successfully put into a steep dive in order to extinguish an engine fire.
This may have been the inspiration for a similar scene in the trailer for the forthcoming "Masters of the Air", where the same aircraft type (Boeing B-17) is also put into a dive to extinguish a fire. (As it is the very first flying scene depicted, I presume it is successful, rather than the plane disintegrating as the weakened wing is torn off, condemning those crew not already burned to death to their doom.)
Wikipedia states that "A dive may also be used as an emergency maneuver, for example to extinguish an engine fire" but provides no sources. Superficially, it makes sense, like blowing out a candle.
I can find only one source which states this was attempted, in a Lancaster in 1943. But the actual citation for the DSO awarded - testimony of a real aircraft fire - suggest that the pilot was actually trying to find somewhere safe to land -

Whilst over the target area, the aircraft was attacked by an enemy
fighter from close range. Its gunfire exploded some incendiary bombs
which had failed to release and a fire quickly developed in the
bomber. The fuselage became a mass of flames reaching through the
mid-upper turret manned by Flight Sergeant Dove. Ammunition in the
turret boxes and ducts commenced to explode in all directions. In
the face of an appalling situation, Flight Sergeant Dove coolly
remained at his post. Although he was burned about the hands and face,
he manned his guns with grim resolution, skill and accuracy. He
delivered a devastating burst at the attacker, which had already been
engaged and hit by the rear gunner and succeeded in destroying it.
Disregarding the roaring flames, he then descended from his turret and
went to the assistance of Sergeant Airey, the rear gunner, who had
been wounded, and extricated him from the rear turret. The situation
had become extremely critical and Sergeant Hazard ordered the crew to
prepare to abandon aircraft. When informed that one of his comrades
was helpless he decided, in spite of the grave risk entailed, to
attempt a forced landing. Meanwhile, Pilot Officer Gates, assisted by
Sergeants Williams and Bain bravely tackled the fire with
extinguishers and succeeded in getting it under control. The aircraft
was now down to 800 feet but, as the fire had subsided. Sergeant
Hazard quickly decided to attempt to fly the badly damaged bomber
home.

A real combat plane fire (source)
Is putting a plane into a dive a recommended, or even plausible, way of extinguishing a fire, or is it an entirely fictional device?

The way it's been shown, as the first and only response to a fire, it's fictionalized, but it's realistic that the pilot might dive.
The procedure for extinguishing an engine fire begins with shutting it down, cutting off fuel supply. Fuel flowing into a hot engine will maintain a fire. "Blowing out" a fire on a running engine by flying faster is not likely to happen. I was perplexed as to why they kept that engine running in the movie, given it was a 4-engine aircraft, easily able to lose one.
Fuel or engine fires cannot even be extinguished by supersonic flight - this report considers fuel fire for supersonic planes a worse, not easier problem.
To extinguish a fire with air, it has to move faster than the flame front, blowing the burning gas, which is hot, away from the combustible material. This removes the heat element of the fire triangle (or tetrahedron).

To do this, you need to push away the entire flame front. Leave one hot item - above the fuel's self-ignition temperature - in the vicinity of the fuel, and the fire will continue.
This works when blowing out a candle, because it's completely in the stream of your breath. Now put that candle inside a protective tube, covering part of the flame, or insert a metal rod that will stay hot, and that won't work.
An exterior fire can be extinguished by flying fast, say if you set napalm on the top of a metal aircraft on fire. Small fires inside a jet engine can self-extinguish, being in a fast airstream. But a fire outside is safe to begin with. Military jets show off by dumping fuel and igniting it with an afterburner, called "dump&burn"; some fuel is left unburned.

If you have an engine on fire, or, worse, a fuel tank fire, the problem is on the inside. What's inside is at least partially shielded from the wind, and will continue to burn.
However, with an older, particularly an air-cooled engine, which have a lot of airflow, it will have the effect of cooling the engine, provided it has been shut down first. That effect can help extinguish a moderate sized fire, like that in the movie. But other steps have to be taken too.

Auto ignition temperature for aviation fuels is around 210C.  If I had no other option I would be inclined to give it a try, certainly if starting from relatively high altitude.

This is a recommended procedure for many aircraft. For example, the engine fire checklist for a C152 goes:

Mixture – IDLE CUT-OFF.
Fuel Shutoff Valve – OFF.
Master Switch – OFF.
Cabin Heat and Air – OFF (except wing root vents).
Airspeed – 85 KIAS (If fire is not extinguished, increase glide speed to find an airspeed which will
provide an incombustible mixture).
Forced Landing – EXECUTE (as described in Emergency Landing Without Engine Power).

Note that it's not dive or land, it's dive and land. If you turn the engine back on you'll likely reignite the fire. In a multi-engine airplane you might be able continue on the remaining engine(s), but you'd likely only do so if the risks of a forced landing are dire.


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Why did the F-4 Phantom have quite so many stencilled messages?
Anyone who has built a model of a US Navy or Air Force F-4 Phantom will know the misery of attaching literally hundreds of tiny stencilled informational notices all over its body.

Eduard 1:48 Tamiya F-4B Decal Sets (source)
Contemporary American aircraft of a similar nature (e.g. F-8 Crusader) don't seem to have nearly as many.
The Phantom appears to be uniquely speckled with info. It might have been because -

The F-4 really did have a lot more access hatches than other aircraft
It had to meet both US Navy and Air Force specifications
The rules hadn't really kept up with the jet age
McDonnell Douglas's workforce was at least one third sign-writers

Was there something physically unique to the F-4 necessitate so many messages, or was it a result of following rules to the letter?

F-4 Phantom II Access Door Decal Set A 1/48 Tamiya (source)

I think more modern jet fighters have equally many hatches but they are used far less often. In general jet fighters requires less maintenance work than before.

Pure speculation: Possibly, because the F4 came online just as the US was entering Vietnam and there were so many people being drafted into service, the labeling was to help fairly new recruits who had received a minimum of training.

I assume you know they’re an aid in locating access panels, exterior switches, etc. for maintainers, feelers, etc. and are instead asking why the F-4 feature them more than models of other type. So, I’ll talk about why the popular image of them seems include so much stenciling.
Obviously, all aircraft always come with them new, but it seems like the Phantom continued to be restenciled much more rigorously than other aircraft during  the ‘70s when, for some reason, F-4s often received complete stenciling after repaints.I am going to venture that this may have been due to a number of reasons:

One or more of the branches flying the F-4 had a dearth of experienced mechanics as many were leaving the service for the private sector or retiring after having joined during WWII, Korea or the start of Vietnam. So, there were a lot of inexperienced mechanics coming thru the pipeline and they wanted the stencils visible for them.

The F-4 might have had a usually high number of access panels, exterior switches, etc. or some might have been close together and could easily be mixed up, especially by inexperienced mechanics.

It could simply have been that whoever was in charge of these decision was a stickler.

In contrast, one AF crew chief said “that most of the stencils were left off the eagles as they were simply not needed and just too time consuming to put back on for minor panels. They only needed them on the most important and most used panels.”
lol,frankly, I wouldn’t want mechanics who needed stencils to do their job working on any aircraft.
This post I’ve found backs up at least part of my theory that it was dependent on branch:
“The F-4s that went through repaint during the fairly brief interval in the early to mid 70s received the stencils. Based on photos from that time that I've seen, the majority of USAF machines never received the white stencils, but there were still a lot that did. They didn't last long either. I joined the Texas ANG in April 1980 and our squadron of F-4Cs had exactly ONE jet with those stencils. By the time I got to George AFB in February 1982 there wasn't a single F-4E or G in the six squadrons assigned to the 35 and 37 TFWs that still had them.” - Scott R Wilson

There's a lot of unsupported speculation ("seems like", "could have been", "I am going to venture") in this post. Good stack exchange answers provide facts supported by references. Not just a bunch of guesses.


text:
Why don't modern military aircraft typically keep their guns covered?
Back in the 1940s, it was common to cover gun ports with tape. As well as improving streamlining, it would presumably help keep them clean.

Spitfire Mk 1, with all eight .303 inch Browning machine guns covered (source)
I suggest it would be fairly straightforward to design a fairing that would immediately disintegrate if the gun were to be actually fired; but, while not in use, prevent ingress from anything unwanted, and provide a small boost to aerodynamic efficiency.

M-61A1 cannon mounted on the F15 Eagle (source)

F-16 M61 Vulcan 20 mm cannon gun port (source)
It's not like these guns are getting regular use. A fairing would seem to deliver a benefit at little cost. What is the reason they're not more common?

It depends on the airframe.  Older fighters from the 1950s-1980s typically faired the gun(s), but left the muzzle exposed.  I suspect the parasite drag from this was minimal in comparison with that created by external stores such as fuel tanks, missiles, bombs, pylons and weapon racks, etc.
Newer fighters such as the F-22A and F-35A, with requirements for very low frontal radar cross sections, do actually use fully enclosed internal guns with a fast acting, faired door over the muzzle.  This actuates to allow the gun to fire, then closes quickly after the trigger is released.

Because the guns are used. In training, fighter aircraft with an air-to-ground mission probably exercise Air-to-Ground deliveries, (including what is called Low-Angle Strafe) several times a month. At least they used to when I was flying F-4s. I would be surprised if it was any less nowadays.
Air-to-Air tasked aircraft (like F-15s or F-22s) may do Air-to-Air gunnery (against a towed target, (we called it a dart back in the day), less frequently. I don't believe these are still in use, they use towed acoustic sensor targets these days. But live fire Air-to-Air gunnery is still done often enough to not make it worthwhile to cover the Gun ports.

Finally, if they did cover the gun ports, and then shot bullets through the covers, there would be the additional hassle of cleaning out all the debris from the gun ports after the aircraft landed.

Re "Finally, if they did cover the gun ports, and then shot bullets through the covers, there would be the additional hassle of cleaning out all the debris from the gun ports after the aircraft landed." -- I'm having trouble following.  Surely the instant the gun is fired, most of the cover is blown away and it's essentially as if it was never there--  assuming we're talking about a "cover" that is more or less equivalent in its bullet-resistance to the pieces of tape in the photo included in the question--

I'm not sure, but I suspect that at 350-450 kias+, the dynamic pressure would be pushing any remaining fragments into the opening the gun barrels were sticking out of.

@CharlesBretana The gas coming out of the muzzle during firing is likely going over 1000 knots.  The ambient air is not likely to push much back in to the barrel.  Even if it could, there cannot be any flow through the barrel because the breech is in the way (unless you have some weird recoilless rifle setup https://upload.wikimedia.org/wikipedia/commons/c/c3/Davis_gun_NARA-45523875.jpg).

I haven't done a complete analysis of this, so I confess my starement is based only on intuition, and might be wrong, but a complete analysis has to consider that the gun gases are only coming out of the muzzle of the gun, which is a considerably smaller cross section of the total area that needs to be covered, the total mass-flow, and momentum, would therefore be equally different.

Just FYI, RAF fighters gun ports were re-patched as part of the re-arming process between sorties - 36 minutes 53 seconds into this video - https://www.youtube.com/watch?v=0rhGrPBDhEA


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Which was the first aeroplane to have fuel tanks within its wings?
Wings with substantial thickness start appearing after WW1, with Junkers pioneering all-aluminium aircraft such as the Junkers F 13 (1919). It as a far from universal trend, however; compare with the  de Havilland Hercules airliner of 1926, which was presumably designed to go as far as possible.
So it seems likely that using the wing volume for fuel must have come later - clearly, simply increasing wing thickness doesn't mean you can start filling it with fuel: there are structural implications too.
Which was the first plane to have a substantial volume of its wings used as fuel tanks? That is, not just the part that is absorbed by the fuselage.

Junkers F 13 (first flight - 1919) - source

de Havilland DH.66 Hercules (first flight - 1926) - source

"RIMOWA The luggage with the grooves". Interesting... are they claiming the Junkers is "luggage"? </OT>

Rimowa is a luggage company, their products have grooves in them. That's probably why they chose the Junkers for their ads.

Start from the Spirit of St Louis and go back from there.


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Can ski-equipped aircraft land on a conventional runway?
These two aircraft operate in the Antarctic: the image shows their undercarriage adapted for the snow. The nearest plane (a DHC-6 Twin Otter) has had its wheels completely replaced with skis. The other (a DC-3 / BT-67) has had a toboggan incorporated under each of its main wheels.

source
The DC-3's wheels protrude below their toboggans, allowing the wheels to support the aircraft's weight on a typical runway. When it flies to the Antarctic, its toboggans are presumably there to stop it sinking in the snow.
However, the Twin Otter is entirely reliant on its skis to support itself. The question is - are planes with only skis capable of safe, regular runway landings? Or are they necessarily restricted to snow?

Yes a Twin Otter on straight skis can land on a bare paved runway... once.
It will then need to be jacked up and the skis replaced with wheels, or at least some kind of trolly gear installed under the skis to let it be moved.  The skis will have to go in to have the bottoms (usually Teflon sheet riveted/screwed to the bottom) replaced.  In other words, it's as if you were downhill skiing and ran out on the parking lot that was bare pavement.  You aren't going anywhere unless you take them off or start walking with them.
If the runway has a layer of compacted snow on it, that is fine and you can land and take off same as on wheels.
If there is no requirement to operate off bare pavement, straight skis are preferable over wheel-skis, like the DC-3 has, because there is a significant weight saving, maybe several hundred pounds, when you factor in the ski raising and lowering system hydraulics and mechanism, and the weight of the wheels and brakes that are eliminated. So if there isn't a bare paved runway to have to deal with, you run on straight skis to get the payload benefits.
There are paved airports in Antarctica, but to the extent the runway is bare surface at times, they will normally maintain a dedicated ski runway of compacted snow nearby so airplanes like that Twin Otter can come and go.  And obviously, the DC-3 can go where it wants.

I would venture a guess that the Twin Otter could handle a grass-field landing and that this would be far less detrimental to landing on pavement of any sort. Might still require ski replacement, but would have a chance of them surviving for a second landing.

Grass would be ok, and if the grass was thick enough, and wet, you could probably take off from it.


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Is it coincidence that the B-2 and YB-49 flying wings have exactly the same wingspan?
Development of the Northrop Grumman B-2 Spirit began as far back as 1979; however, this was nearly thirty years after the last flight of Northrop's earlier flying wing the YB-49.
There aren't many apparent similarities: engine position, wing-sweep, shape and control surfaces are all different. Yet they have identical wingspans of 172 feet or 52.4 m.
Is there something special about this particular size? Did Northrop mutate their earlier design (through wind-tunnel testing etc.) from one to the other, or is it purely coincidence?
 B-2 source
 YB-49 source

A random guess without any supporting information. (please edit or delete if this turns out to be inaccurate)
I would guess the logistics of manufacturing. It could the space needed for handling the aircraft in and/or out of manufacturing buildings.
The B-2 program was wildly expensive due to the large number of new technologies involved.
So I guess it was a prudent, maybe even progam-saving decision, to use existing manufacturing facilities are far as possible.

No. You design the aircraft first, then you build or modify the production & assembly facilities to manufacture it. For something as unimaginably expensive as the B-2, designing it so that it could be built on a decades-old production line, with entirely new technologies for literally everything, would be thoroughly pointless. (Besides, the YB-49 wasn't exactly mass-produced.) For a vastly different scenario, this might happen, but in the case of the B-2, no.

Northrop Grumman has buildings only that big. While you need to design a new production line for a new plane, why don't use existing buildings? I do not claim that this is the true reason, it's speculation on my part. There are many constraints one new designs, be it airplanes, rockets or ships, and some of these constraints derive from the surrouding, supporting infrastructure. E.g. US warships are designed to fit the Panama canal locks, while the Bismark or the Yamato were free of such constraints.


text:
Why do modern airliners have windscreens which open?
I'm sure it must be nice for pilots on a hot day to pop open their windscreen while waiting on the tarmac, but is there a good engineering or safety need for them? There must be a significant amount of cost and time effort in making a windscreen both openable and safe. If the pilots really need some fresh air, they're usually pretty close to the passenger door.
I can imagine there were valid historic reasons for having them: when planes were smaller and instrumentation not so sophisticated, you might literally want to take a proper look at your propellers spinning before setting out. But why do we persist with them?

737 Max with both its cockpit windows open source

Airbus A380 with open window source

It harkens back to the railroad practice of passing up train orders while in motion. Obviously this stopped working the moment they put engines on the wings, but the FAA never changed the rule.   Is that what you're expecting to hear? :)

Not all modern aircraft have windows that can be opened. The Boeing 747 for example does not.
On the Boeing 737, the windows can be opened for two reasons:

Emergency Evacuation: When the aircraft needs to be evacuated, there is always a way to escape from the flight deck without going through the cabin. On the Boeing 737, this is accomplished through the windows. From the 737 NG FCOMv2 (1.40.30):

The flight deck number two windows can be opened on the ground or in flight and
  can be used for emergency evacuation. To open the window, depress the trigger
  and turn the handle back and inboard. After the window moves inboard, move it
  back until it locks in the open position.
[...]
Flight Deck Window Emergency Egress
If the flight deck number two windows must be used for emergency egress, use
  the following procedure:

open the window
open the escape strap compartment (above and aft of window)
pull on the escape strap to ensure it is securely attached
throw the strap out the window
sit on the window sill with upper body outside
exit in accordance with the following illustration.

CAUTION: Ensure the escape strap is securely fastened to the airplane.

Aircraft without windows that can be opened, have an escape hatch in the ceiling. You can see the 747 escape hatch in the following image from the FCOM:

Smoke or Fumes Removal: If there is a fire in or near the cockpit that cannot be easily extinguished (e.g. fire in the electronics behind the screens), the smoke has to be removed in order to continue to fly the aircraft. This can be accomplished by opening a window. From the 737 NG QRH (8.19):

Smoke or fumes source is confirmed to be on the
  flight deck:
Caution! Window should not be
  opened unless the source is
  confirmed to be on the flight
  deck.
Establish normal holding speed. High
  airspeed may prevent opening the window.
Open the first officer’s sliding window.

On aircraft where the windows cannot be opened, there is a dedicated system to evacuate the smoke, e.g. from the Boeing 747-400 QRH (8.43):

Smoke or fumes persists or is severe and the smoke or fumes source is determined to be on the flight deck:
Pull the smoke evacuation handle. Pulling the smoke evacuation handle when smoke or fumes source is not on the flight deck may bring the smoke or fumes into the flight deck.


text:
Which aircraft have fought against its own type in active combat?
The criteria for this question are

The aircraft has to be the same type (but not necessarily the same mark)
The two opposing sides are actively hostile; but not restricted to nation states (so civil war a possibility)
The aircraft treat each other as an active threat
Cloned aircraft count, e.g. Tu-4 / B-29 or J8M / Me163 (neither of these occurred as far as I know)

It's difficult to see circumstances in which it would happen; but in over 100 years of air combat I think it likely to have occurred at some point.

Perhaps in the current Syrian conflict against Russian Air Force fighters? No actual dogfighting.

After some research I was quite surprised that all those few thousand Mig-19/J-6 and Mig-21/J-7 (possibly) never fought among themselves, although Pakistani J-7 did shot down an Indian Mig-21 in 1971. Maybe J-7 fought against Min-21 in the Uganda–Tanzania War and Iran–Iraq war but I can not find any source on that, none confirmed shot-downs at least.

Probably not the only situation, but in 1948 Israeli Spitfires faced Egyptian Spitfires, and just before the truce also faced a few RAF Spitfires that were too close to the combat area (reference)

I think this is the best instance of same-on-same encounters.

Captured aircraft being used for evaluation is quite common, but I can only find one instance of them being redeployed actively: during the Spanish Civil War. Among a number of aircraft that were captured by the Republicans was a squadron of Fiat CR.32:

During the war, the Republic captured at least 11 Fiat Cr.32; some of
  them were captured when the troops occupied anbandoned airfields, one
  more when its pilot deserted, three when italians pilots landed in
  enemy airfields and another one rebuilt at La Rabasa using wrecks... The Cr.32 that stood [remained]
  in Spain were transfered to 71 Group, used to defend Alicante.
  [source]

It's possible they went head-to-head with the Aviación Legionaria CR.32s; I think it's safe to say that the opposing air forces were both using the same type of aircraft in active operation.
Here's Spanish Republican Air Force ace Manuel Aguirre López in front of his captured CR.32 - the printed caption says

the aircraft is often flown by Aguirre himself

He's credited with shooting down a number of CR.32s himself, although none while flying his captured CR.32. source

source

There was an account of Soviet MiG-17s engaging in a fight with Hungarian MiG-15bis in 1956 (I could only find an archive quote now). They ended up crashing into each other (whether deliberately or not) in the Austrian airspace.
This might formally not qualify, but arguably the difference between MiG-15bis and MiG-17 is smaller than between, say, F-15A and C, or even between Tu-22M2 and Tu-22M3.

I'm late to the party, but during the 1969 Football War Honduran and Salvadoran Corsairs went head-to-head. Technically the Hondurans were flying Vought F4Us, while Salvadorans were flying Goodyear FG-1Ds. Honduran pilot Fernando Soto ended up shooting down a Salvadoran P-51D from his F4U Corsair. Later the same day he made a diving attack on two FG-1D Corsairs, destroying the first in a high speed pass and the second in a dogfight. As far as I can tell, this is also the last piston-engine dogfight to have ever taken place.

One story originally told by Martin Caidin in his book on the P38, was the tale of the phantom P38, one that had been captured by the Italians and was flown in US colors by one of their pilots, Guido Rossi, to shoot down stragglers after coming in close under the guise of being an escort.
Supposedly, this morphed into a struggle between Rossi and one of his victims, Lt Harold Fischer, who survived the shoot down. Fischer requested a YB40, a B17 with a lot of extra guns and ammunition, to go hunting Rossi. Fischer went so far as to find Rossi's wife, who was living in Allied controlled territory, and paint her picture and name on the YB40 to draw Rossi in, and eventually shoot him down. Both survived the war. When Fischer died as the result of a crash during the Berlin airlift, Rossi was at his funeral.
The way the story is told has elements of 1940's fiction about it, so it may have 'grown in the telling'. But, like a lot of wartime stories, it probably derives from an actual incident.
Interesting side story that came up while looking into this... the 500 round belts of ammunition for the M2 50 caliber machine guns on the B17 and B24 were 27 feet long. Supposedly, the expression 'give them the whole nine yards' derived from a bomber gunner dumping an entire belt of ammunition at an attacker.

Nice story about the whole nine yards. The phrase was first used in the 1850s, which would indicate the B17 is older than most people realise. ;)

And as far as the phantom P-38 goes, the story beggars belief. Rossi is said to have shot down multiple bombers over a period of weeks, but where would he get the ammunition? A single shoot-down would generally require much of its entire supply (averages on the B-17 required >25 20mm or hundreds of 13mm). And then how would US intelligence possibly learn who he was, or where his wife was, or get an image of her? I'm sorry, but this strikes me as yet another tall tail Caidin was credulously willing to spread, like the surfing B-17.

It will probably be a while before we get any reliably definitive proof, but the current  (2022 - ??) "Special Military Operation"/un-provoked invasion of Ukraine by Russia pits ex-Soviet aircraft of various types against similar ex-Soviet aircraft on the other.

Starting with Wikipedia Ukraine has Mig-29, Su-24, Su-25, Su-27. On the Russian side , all of those are listed as "in service". So it comes down to researching the air battles to see what's happened.

I recall that Hungarian and Romanian He 112's were active at the same time during their minor tiff over Transylvania, although I doubt they met in combat.
Various PZL designs ended up used throughout the area, so I would not be surprised if they were also operating against each other.


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Help identifying airfield and aircraft from movie "My Spy"
Here's a couple of stills from the movie "My Spy" - the climactic scene takes place at a single-strip airfield with a paved or tarmac 09 runway.
My tentative identification of the (clearly unflyable) military planes in the background, from left to right: an Avro CF-100, a F-86 Sabre, then a two seat F-104, and next (judging from the tail) another single seat F-104 in unusual light green camouflage.
The red and white plane in the background, from a later shot, is an F-5 in unusual livery.
The second picture points to the F-86 being RCAF, which would point to a Canadian airfield. On the other hand, the furthest F-104 looks very much to be in Belgian colours.
There's not much more to go on! I wondering where this is, and how these planes ended up there.

"My Spy" 2020 Amazon Films / STXfilms

The film was shot in and around Toronto, so a search of local airfields on Google Maps led me to Markham Airport. From there, Wikipedia provided this list of military aircraft on the field:
CT-128 Expeditor transport
CT-133 Silver Star
CF-5 Freedom Fighter
CF-104 Starfighter (Various Airforces)
Canadair CL-13 Sabre
Schweizer SGS 2-33A Royal Canadian Air Cadets[citation needed]
Noorduyn Norseman - shell only
The aircraft belong to the Canadian Air, Land and Sea Museum. Looking at the satellite image on Maps it would appear that a number of other aircraft have been stored there, but have now been removed.
There's a clutch of rather more complete airframes in amongst the buildings in the south west corner of the airfield.

Google Maps

I might be a little late to the party, but my daughter just convinced me to watch this movie a couple of days ago and, being RCAF for the last 30 yrs, I noticed the red & white CF-5 right away. It’s an old 419 “Moose Sqn” colours bird. I saw it several times when I was posted to Cold Lake, AB. Sad to see these old hulks in such disrepair.

“My Spy” 2020 was mostly shot in the Toronto area and the airport scene was shot at the Markham Airport near Toronto.

By picking a different part of the airport to grab a screen shot of, they could be totally different places on Earth!


text:
When aircraft rolls across airport field, uses its main engines or any kind of chassis gears?
Taxiing, turns, approach to gates - everything is done without the loud sound of motors

It's unfortunate that this has been marked as a duplicate since I can't now add a different answer. Air India and Lufthansa are now making use of taxibot, an Israeli developed system employing a pilot-controlled, semi-autonomous tug to tow aircraft to and from the runway.

@CatchAsCatchCan If the OP is interested in that, they could edit their question to ask for alternatives and we could then vote to re-open the question. As it is right now, the question does not ask for alternative systems, so you should not answer.

@cathascatchcan you may add information on the other (original, not duplicate) question

Main Engines, and braking with wheel mechanical brakes.
Main engines at low power are used to move on the ground, that's why usually planes can't move backward, unless the engines are capable of reverse thrust.
And for ground maneuvering planes uses wheel brakes, as other land vehicles.

ofc, i will update it

Most larger aircraft (including regional propliners) are capable of reverse thrust, but this is avoided because the wash potentially hurling heavy objects in front of the plane around and breaking terminal windows.


text:
Can any US airline fly to and from any US city it wants to?
I am trying to understand the US commercial aviation industry. Assuming that slots are available, are US airlines permitted to fly to and from any US city they want to? Or are there limited permits issued by each city/state that limits the number of airlines that can serve an airport/city/state? For example, if I start an airline based in New York, is it simple to get permission to fly between San Francisco and Anchorage (assume that slots are available)? Were there any restrictions before the Airline Deregulation Act of 1978?

Before and after airline deregulation are so different that it's almost like asking about two completely different countries, and would merit a separate question.


text:
Why is waste water from lavatory sinks dumped outside in mid-flight?
I learned that the waste water from the lavatory sink in most commercial airliners is dumped outside the aircraft while in flight. Is this really the case? If so, why is the waste water dumped outside instead of being stored in the septic tank together with the waste from the toilet bowl?

Consider what happens when half a litre of slightly unclean water is dropped from an aircraft travelling at Mach 0.85 and 35000ft.  What hazard would you be concerned about?

Where did you learn this?

As a side-note, I dimly recall an article in the New Scientist dating back probably to the late '70s.  It seems that until that point it was routine for raw sewage to be dumped overboard, but questions were raised as to whether diseases could be transmitted that way and the practice was stopped, although I'm not aware of any direct evidence that it was a problem.

@RetiredATC I found some possibly pirated PDFs of training manuals for the Airbus A320 and Boeing 737 which described their water and waste system (ATA chapter 38). The diagrams appear to show that the water from the lavatory sink goes out of the airplane without being collected in some kind of storage tank.

Fun fact: it is the same on buses (not the Air-type). At least the ones I worked on.

Kind of makes me wonder if it's possible for a plane to run out of fresh water for the taps on a long flight if people are using it too much?  I get there's a reason the faucet handles are spring-loaded, so they won't stay on unless you're holding it with your other hand.  I guess the only alternative would be a water-recycling system like they use on spacecraft, but that's probably a bit much for a plane.

Every now and then there's a Blue Water leak and "sanitary" waste freezes and falls to the ground like a cannonball: https://en.wikipedia.org/wiki/Blue_ice_(aviation).  Traditionally, trains just flushed out onto the tracks (I don't know if they still do).  There were signs telling you not to flush when the train was stopped, even a well known song (well, known to the train-going generation before me): https://lyricstranslate.com/en/oscar-brand-humoresque-passengers-will-please-refrain-lyrics.html

@Flydog57 no, getting retention tanks was the first thing Amtrak did as they started to get their own new-build coaches. Also after they culled all their old inherited heritage coaches down to ones worth keeping, they rolled them all through Beech Grove and retrofitted tanks and a bunch of other tech. Even the heritage museums use tanks now.

@Flydog57 You could actually look down onto the tracks through the toilet bowl drain opening.

going sci-fi, I wonder if airborne pathogens discharged through grey water can be scooped up by aircraft flying the same path (cold air and water droplets seems to be a good way to preserve microorganisms and pathogen). Luckily, there is a simple solution to this issue: toilet users should wash their hands without touching their hands and before washing their hands :D

@DarrelHoffman - "Kind of makes me wonder if it's possible for a plane to run out of fresh water for the taps on a long flight if people are using it too much"  Yes, obviously, of course, certainly.  It doesn't happen often, but it happens.

@DarrelHoffman whether the water is dumped directly or stored in a tank has no bearing on whether the plane might run out of fresh water to be used.

“Grey” water from the lavatory and galley sinks is dumped overboard through electrically heated drain masts.
It is much cheaper and simpler to drain it overboard rather than store it. Dumping it also makes the aircraft lighter and more fuel efficient as the flight progresses………..
(better carbon footprint?)

Between flights it drains onto the ground or unsuspecting ramp workers under the aircraft. In cruise flight the outside air is cold enough for the water to freeze instantly and form small contrails.
There are many photos online showing these mini contrails that form briefly while the water is actually draining:

+1 These photos also show clearly that the amount of water involved in the grey water disposal is insignificant compared to the amount of water vapour produced by the actual engines.

Are you sure that none of those photos are showing the contrail from the APU, rather than from a gray water drain mast?

The Emirates 380 could possibly be an APU but it is highly unlikely a 4 engine aircraft would need to operate an APU at cruise altitude.  The other 2 are very obviously not APU as you can see where the mini contrail exits from.

@MikeSowsun on the dot - weight is fuel efficiency. With no negative effect of dumping the water overboard.... why not dump it?

Reverting to my 13-year-old self, the plane is peeing.

@quietflyer you can see in the first and last image that the contrails originates from the grey water disposal and not from the APU.

@GregHewgill the amount of water involved in the grey water disposal is insignificant next to the power of the Force.

The lav sink is what is known as "grey water" in a house water drain system.  Not sewage, just water with dirt and soap, and maybe toothpaste and mouthwash in it.  It goes overboard through a heated drain mast, and just evaporates, the solids in it becoming dust to the wind.
Don't go peeing in the sink, and you won't be creating any problems.

Even urine will evaporate and disperse into the atmosphere.  A turd is another story altogether....

Yes but you wouldn't want to be the one that had to work on the drain mast to fixe the heater or something lol.

A little biochemistry remindment: urine happens to be a sterile water-saline solution with some sulphur-based water-soluble compounds solved in it, and some acids for getting the right pH. All of the forementioned make it a perfect environment for grow of bacteria and fungi which both happen to be everywhere, which will soon start spoiling this solution. There's no lipids (fats) in urine, though. So if any other, less microbe-growth-friendly water solution will dilute the urine, it'll be just like... any other water solution, with nothing special on it both biologically as well as chemically.

@JohnK Read my previous comment (ran out of char limit), and also keep in mind that the greywater would have pretty big amounts of detergents like soap, mothwash and so on, making the mixture requiring far far less other water to deprive the urine all biological urine proprieties.
Planes are engineered very carefully and precisely, you know? :D

@MobileDevelopment Are you saying that the waste water from the sink should be stored together with urine from the toilet to reduce bacterial growth?

@flux I don't know whether "should it" or not, and I think that your question/statement should be inverted to make more sense logically "the urine from the toilet should be stored together with the waste water from the sink", and then, the answer is: Yeah, definitely It'll reduce bacterial (and other microbes) growth. Watch temperature and some other thermodynamic parameters with you mix it, tho - it'll be able to optimize reducing the microbial growth even more.

@MobileDevelopment urine is not actually sterile, it just turns out that what is there is generally not picked up by standard culture techniques. There was a lot of papers 2012-2015 or so about it.

Urine is in no way sterile, even in healthy humans. And even if it was sterile in the body, the urethra is probably not sterile either. And of course, not everyone is healthy.

@MobileDevelopment Definitely not sterile if you have a UTI!

First, it is not just lavatory sinks, it is also (as per this Airbus patent):

the condensate of the cargo spaces and the outer doors, as well as the
washwater of all of the hand wash basins and accordingly, has
contaminants (such as soap, for example) as well as colored
contaminants, such as kitchen waste, like coffee, tea, or juices

If you think about it there's only so much room in an aircraft. The aircraft already stores:

Clean/Potable water
Black water (i.e. human excrement from the toilets)

The amount of clean water on-board is larger than the capacity of the black water tank. There is a reason why aircraft toilets flush using vacuum and not water !
Also storing it on-board means more weight, which means more fuel required. You also have to remember that whilst aircraft can take-off "heavy", they cannot land "heavy".
If you think about a very large aircraft like an A380, the amount of additional storage capacity would be enormous !
Finally don't forget airlines are a commercial business. Taking more space for grey water storage menas less space for cargo means less $$$ for the airline.

I'm not sure you're correct about aircraft not being able to land heavy, at least in the context of water storage.  Burning fuel will make aircraft light enough for landing to be possible.  If an aircraft was borderline too heavy to land again right after takeoff, most of the weight of consumables would be fuel, not water.  With a full load of water but only a partial load of fuel for a short hop, the plane wouldn't be close to its max takeoff or landing weights.  (Correct me if I'm wrong).

So the important point here is efficiency; smaller tank needed, and getting to dump some water weight during flight.  (Or not needing a separate tank if they wanted to keep gray and black water separated.)  As you say, a tank would take space, and its walls would have some mass, and would still need a way to be drained after landing.

@PeterCordes The other factor in play is balance. With only so many places you could put a bigger/extra waste tank, on a closed system (i.e. no grey discharge) you could end up with a severely out of balance aircraft as a result of a substantial amount of weight being shifted from one location to another.  You don't have the luxury that you do with the fuel where the fuel can be rebalanced between tanks.  Rebalancing waste tanks would likely lead to blockages !

Good point.  And the weight of pumps is hardly justified for something that isn't safety critical like fuel management.  So it would become an extra engineering constraint.  Although perhaps you could design fuel tankage to balance it, if you already have a mechanism for fore/after CG shift by pumping fuel.  Except you don't want that fuel pump to become necessary for safety if you can help it...  So yeah, clearly some secondary downsides if you couldn't just vent graywater.

@PeterCordes You could use the grey water to flush the toilets. Some experimental residential water preserving systems do that. One typical problem with that is microbial growth in the grey water, and of course the overhead for grey water storage on the plane.

Just waiting for one of the budget airlines to charge you extra for going to the bathroom... after all, you carried that extra weight onto the plane (or ingested it after getting on) which means it took extra fuel to take off and get to cruising altitude with that weight...


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What is the cost per hour of a Gulfstream V?
Could someone inform me about the exact operational costs of a flight hour for this specific type of aircraft?


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What are the best tips for circuit practice with strong crosswind?
I am a student pilot with around 30 hours of flying right now. I am yet to solo and I am currently in the final stages of closed circuit practice.
Overall, my pattern work is good. However, maintaining the perfect "rectangular" circuit gets tricky for me when facing strong quarterly crosswinds (10 knots gusting 16).
I guess its the visualizing the wind that really gets me confused. I set the heading bug to sort reference where the wind is coming from which helps a lot.
But just wondering if I could get more tips on this. Anyone else had the same issue during their student days?
I fly a Cessna 172S.

If the problem is keeping the pattern rectangular you should work on ground reference maneuvers - turns about a point and S-turns across the road.  Then go out and find an area where there's a set of rectangular streets (or at least one straight street that you use to simulate the runway) preferably on a windy day.  Then practice flying directly over the rectangular ground path.  Don't worry about the wind or your actual heading, just steer to keep the plane over the path.  That should help ingrain the response.

Try visualizing the pattern.
In your mind's eye, overlay the airspace around the airport with the track that you want your flight to take, visualizing all sections of the traffic pattern from your point of view as you fly.  Now check to see if there are visual references on the ground eg buildings, roads, parks, golf courses, etc. which align with this pattern you are visualizing and use them as additional aid for pattern legs and turn points.  If the airplane drifts off this track, adjust your crab angle and/or your rate of turn in order to track correctly.
As mentioned above, ground reference maneuvers such as rectangular patterns, turns about a point, S-turns etc are very useful and may be good basic practice for training yourself to visualize the pattern in space.

Thanks sounds good! I will discuss this with my instructor. Thanks a lot everyone!


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Do some aircraft windshields contain gold particles?
I've heard that the windshields of some aircraft have gold particles, but I don't know why?

Agreed - the F-22 question could do with a more general title, and we'd be done.

actually, @egid, it question the F-22 question is a dup of could use a more general title and all would be good. :)

And FWIW, gold particles (at least in low concentrations) make red/ruby colored glass: https://en.wikipedia.org/wiki/Glass_coloring_and_color_marking#Striking_glasses

@Rodrigo de Azevedo: The point I was trying to make is that (as with the F-22 in the link) a gold COLOR is not necessarily (or even probably) produced by actual gold.


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What should I do if the FAA requests health records that no longer exist?
I am working on obtaining my FAA Medical Certificate and I was deferred.  I received a request for more information and one of the items that was requested were medical records related to a surgery I had as a young child over 30 years ago and the records no longer exist?  How can I resolve this?

I had a very similar situation. Along with the documentation they requested that was available to me, I submitted a letter explaining my lack of the older records. This was apparently acceptable to the physician reviewing my case because I was issued a third-class medical cert. You can borrow from the verbiage I used (identifying information removed):

I am unable to provide any medical records or previous imaging related
to the injury in question. I contacted the hospital that treated me,
[hospital name] in [city, state], and was informed the records have been
destroyed. [State] law [citation of statute] requires retention of records
for “[quote document retention language from the statute].”
The injury and treatment occurred in [month] of [year].
[Hospital name] does not retain records past this requirement, and
the records you are requesting were destroyed more than 10 years ago.
Furthermore, the physician who treated me, [physician name], is no longer
practicing.

Good luck!

Thanks, this is really reassuring.  I'm still trying to get ahold of either the regional flight surgeon's office or the national aeromedical certification division to get a concrete answer, but this seems pretty promising.

I was able to get ahold of the aeromedical division today and they said the same thing.  Officially, the best bet is to get a letter from the hospital or from your doctor saying the records don't exist, but even just writing it up yourself is often sufficient.  They said they like to have them if available, but if not, they understand.

I had a similar issue. The original records no longer existed, so the FAA requested a new assessment of the condition and whether any further treatment was required. The doc wrote up the history I reported and “no further treatment required”, and the FAA dropped the matter.

A small tip when sending copies of your records to the FAA or anywhere else:  Read every page first before you send them to ensure they are yours.  I did this and found several pages from somebody else's.  Remember whoever is doing the copying is just going to copy whatever is in the file which may contain mis-filed items.   Or, whoever copied your records may have allowed somebody else to copy "just these few pages" and some of them ended up in your batch.


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What happens to used deicer fluid?
I noticed several tanks at BWI that store waste deicer fluid. They're in the foreground of the picture; the tanks in the background store Jet A.

What do airports like BWI do with deicer fluid after they collect it? This question is similar but it only partially answers my question. Is the fluid treated the same as household wastewater?

Generally it enters the ramp drainage system and flows out with the rest of the runoff. Sometimes its recycled and sometimes its just filtered out of the runoff water and disposed. The EPA has a lengthy report on it you can find here various airports have different methods for recycling it or filtering it out as well as water drainage systems that vary in complexity and scope. The report sheds some light on the various systems involved at different airports.

Longer blurbs are available in the report (see section 7-1) for deeper descriptions.
Ultimately the components of De-Ice fluid break down fairly rapidly when released.

When released into the environment, both ethylene glycol and propylene
  glycol are expected to partition to surface or groundwater. They are
  expected to rapidly biodegrade and not to persist in the environment.
  Biodegradation rates depend on temperature and oxygen conditions and
  glycols biodegrade more slowly under anaerobic conditions. The
  half-life of ethylene glycol and propylene glycol in water under
  aerobic and anaerobic conditions, and in soil are shown below. Note
  that these data were not conducted under the same laboratory
  conditions and may not be directly comparable (5).

Smaller fields or those that can not afford complex systems may allow it to flow into installed drainage systems right off the ramp. The small field I fly out of has no formal system to dispose of it.

Thanks! That answers my question quite nicely.

For those curious POTW means Publicly Owned Treatment Work, i.e. a sewage  treatment plant.


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Do airport fire departments have to have airstairs?
On the video of the JetBlue 292 landing (at 4:27), one of the first emergency vehicles to approach the Airbus is a fire department airstair. I've never seen a fire department with its own airstair. I found a standalone picture of LAX's Stair 80. I don't see a stair among ORD's fire apparatus but DFW and DEN have them. Why do some airports apparently have airstairs but others don't?
The only reference I found from the FAA is a 2012 article about New Large Aircraft (e.g. A380). Relevant passage:

Several airports are now acquiring mobile air stairs and modifying
  them for ARFF use with hand lines, ventilation equipment and fire
  fighting tools. Some European airports have even acquired customized
  platform vehicles for rapid firefighter access into aircraft. Ideas
  being discussed are various air stair designs, scissor lift catering
  style trucks and modified ARFF vehicles with stairs or ladder that
  will accommodate all sizes of aircraft, including double deck designs.

I found this manufacturer page touting the importance of fire department airstairs. So obviously they exist. Here are my questions:

Does the FAA require fire department airstairs?
What are the primary uses? Getting passengers out or getting firefighters in?

I don't think they have to own airstairs but they have to have access to them, or some other means to get onboard

Sorry unfamiliar with FAA regs, but since Canada's regs are often just rewrites of US or ICAO rules:
In Canada, I cannot find any direct reference to airstairs as required minimum firefighting equipment : Canadian Aviation Regulations (SOR/96-433) section 303.09
there is however a requirement for holding an airport certificate in Canada requiring a safety management system be in place, this involves doing a detailed risk assessment.
logically having the ability to deplane any aircraft expected to land might be seen as a necessary risk management solution to a number of potential possible issues. There are similar requirements for "air operator certificates", meaning some of the accountability may be place on the airline. Like so much of Canadian law, we will probably not get a definite answer until a large number of people die and the courts get involved.


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What's the shortest amount of time a commercial airplane will be on the ground in between flights?
What's the shortest amount of time a commercial airplane will be on the ground in between flights?
After a commercial flight lands the passengers and luggage have to be unloaded, the airplane needs to be refueled and undergo mandatory inspections, etc.
With all of that going on between a commercial airplane's landing and takeoff, what's the shortest time it would take between flights?

Plenty of the flights around Orkney are timetabled for five minute turnarounds, looking at both ends of the world's shortest flight.

Well, if the guy touches down and sees a luggage tractor on the runway, then the time spent on the ground will be extremely brief.

@TylerDurden Yeah, the shortest amount of time an airliner spends on the ground between flights is about this long. I count about 3 seconds.

It greatly depends on the size of the aircraft and type of operation... An A320 or 737 sized aircraft can be turned around in about 25 minutes if everything goes well

Related: http://aviation.stackexchange.com/questions/30216/is-there-a-legal-minimum-stop-time-between-2-legs

Does go around on the runway counts? Then less than a second.

There have been cases where a plane lands, drops off a passenger, and then takes off again ASAP and reports a missed approach to ATC to avoid having to re-file.  Of course, people won't be able to pull off that old school cowboy-pilot stuff like they used to once we have ADS-B in-full by 2020.  *Word of mouth only.

I flew SA-226/227 Metroliners for two different commuters back in the 1980s. If we were behind schedule, station managers had the option of asking the pilots to do an engine-running turn. The passenger entry door and the cargo door were on the left side of the airplane, so that meant the right engine was left running.
Such turns, usually only requested if there were few passengers exiting and entering, and little baggage being unloaded and loaded, took as I remember less than 10 minutes. The Metroliner was very noisy even with only one engine running and you didn't want to do it if any kind of a line would form at the bottom of the entry stairs.
Captains had the option of refusing such turns, and some captains wouldn't do them.

How much faster do you actually get the second engine running again when you can directly tap on bleed air from the other?

Why does leaving one engine running shorten the turnaround time?

@leftaroundabout Metroliners were powered by Garrett TPE331 turboprop engines. They had electric starters, not pneumatic starters. Interestingly, this same engine was the APU in the 747 and other Boeing designs.

@PeteBecker Leaving one engine running removed the need to position and connect a ground power unit and then disconnect and get it out of the way after starting. And, since the Garrett engines were direct-drive (a single solid shaft) they took more time both to shutdown and start than, say, PT-6s with two shafts rotating independently, so leaving one running saved you the time for that engine. They also had to have the prop rotated shortly after shutdown, so you  saved that time as well. Ground crews were minimal at out-stations, often only two people, and sometimes just one.

My personal record in commercial flying is 5 minutes block-in to block-out. At that job, typical time was 10-20 minutes on blocks. Actual time on the ground for such a stop typically included an additional 5 minutes for taxi and checks for a total of 10 minutes on the ground.
I did not typically carry passengers at that job, which aided in the short turn-around time. Time on blocks will typically increase with the number of passengers carried.

What the heck were you carrying that you were on the ground for such a short amount of time? If you hadn't said commercial flying, I'd have though you were flying a C130 with the boys pushing the load off the back ramp as you ran down the runway...

@FreeMan We weren't usually carrying cargo or passengers; the aircraft was an aerial platform.


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Does the Garmin G-1000 contain a database of airport information?
Some modern avionics contain airport information similar to what is published on charts and in the FAA's Airport/Facilities Directory.
Does the G-1000 keep airport information in a database that can be accessed by the pilot and displayed on-screen in flight?

Yes. Airport information can be displayed on the MFD under Waypoint Pages (WPT).

Thanks Chris.  On a side note, do you fly one regularly?  Would you mind checking something specific for me?  (there's a tie-in with my two recent questions...)

@MichaelHall I do not, no.


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In what conditions are visible Wingtip vortices created?
If I would want to create a visible wingtip vortices on a given plane, what are the conditions that I would need to meet?
Wikipedia gives the following explanation:

The air cools adiabatically in the center of the turbulence at the end of the wing, as this is an area of particularly low pressure. The air often reaches temperatures below the dew point temperature, which leads to the condensation of the water in the air to water vapor / mist and a vortex is visible. When approaching with moisture-saturated air, you can see such vortex heads even at several points on each wing, in addition to the outer edge often, for example, at the respective end of the buoyancy aids (flaps).

Now to the question:
What conditions would be needed the have them built on a oltimer plane like the Douglas SBD Dauntless or the Douglas TBD Devastator?
I would assume Ideal conditions would be a tropical climate near the Ocean with a high humidity near ground level.

Related: Can these vortices be dangerous?

Wingtip vortices form because of the finite wing span effect, i.e., near the wingtip the high pressure under the wing can no longer be effectively contained and bleeds off to the low pressure above the wing, thus creating a swirling motion of the air. The swirling motion creates a large centrifugal force near the core region of the vortex, i.e. the point around which the entire vortex revolves, and this rapidly expands the air near that point, and with adiabatic expanding comes adiabatic cooling, sometimes to the point that the air temperature drops below the dew point, thus the condensation.
Now the answer is pretty obvious. You don't need a jet to produce a visible vortex. In order for the vortex to be visible with condensation, the vortex must be strong and the air must be moist. A strong vortex suggests the pressure difference above and under the wing must be large, which means the wing is working hard to generating a lot of lift. Even on an old little plane, just fly it low and corner as fast and hard as you can. That's when vortices typically manifest. Of course, you can deduce from the above that an airplane with higher wing loading will show visible vortices more often that one with low wing loading.
Jets typically have higher wings loading because their airspeed is much higher, and according to the lift equation, $L=\dfrac{1}{2}\rho v^2AC_L$, we get $\dfrac{L}{A}=\dfrac{1}{2}\rho v^2C_L$. If your $v$ is higher, with $C_L$ not differing much, you generally get higher wing loading.
The wiki is correct in saying that wingtip vortices are not limited to wings. Ailerons, flaps, rudders, elevators all have their own vortices. A quick search on google will yield hundreds of pictures of fighter jets with 5 or 6 vortex trails attached to it. Of course, you don't see more than 2 trails on large airliners very often because they don't maneuver crazy like fighter jets.

In take-off and landing, seeing multiple vortices on larger (commercial) aircraft is quite common. See e.g. these pictures of an MD-11 with a vortex generated from the TE flaps and an A380 and B747 showing vortices from the engine nacelles.

It would be excellent answer if it wasn't for the first two misleading sentences.

You're definitely right about humidity, but from experience I'd say a colder environment works better than a warmer one. Case in point: unstable/rainy autumn weather (as common in Northern Europe) shows (tip) vortices very well, whereas I haven't seen them so much in hotter places (Southern USA, Caribbean). Having ensured visiblity, a larger pressure difference between lower and upper side of the wing (caused by higher speed and higher lift force) increases the tip vortices in size/strength. This explains the fact that (wake vortex) separation minima are largely dependent on aircraft mass (which scales with lift).
Additional (or stronger) vortices can be created artificially using vortex generators. As turbulent flow separates less easily than laminar flow, these are used (on wing leading edges, engine cowlings, tailplanes) to trigger turbulent flow and thereby prevent/postpone separation. This is especially important if there are control surfaces (such as ailerons or a rudder) downstream, which lose their effectiveness in separated flow. In theory, you could use this same principle to increase vortex visibility.
Whether this also works in theory of course depends on safety standards and regulations concerning modification and the size of the vortex generator required. Examples from the world of sports aerodynamics, where surface roughness or 'transition strips' are integrated in suits worn by speed skaters or cyclists. As you can see on the images in the linked article, these are fairly small.

vortex forms in winter more readily because the ability of air holding moisture decreases with colder temperature, so the winter air is a lot closer to the dew point than the summer air, although in terms of absolute humidity air in winter is  much lower than air in summer


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Can I descend during downwind or I can only descend when I am at base?
If I am close to the end of downwind, can I commence a descend first or I must make a turn first, e.g. leaves downwind and enter base, before I can descend?
Is there a official reference to support this?

Assuming you're in the US and asking about helicopters (as per your tag), this question is very closely related

I agree with the answer below of 'depends on kind of aircraft' but believe there's many other factors.

See Chapters 7 and 8 of the FAA's Airplane Flying Handbook.
https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/airplane_handbook/media/10_afh_ch8.pdf
The descent point for the approach is going to be largely based upon the handling characteristics of the specific type or model of aircraft you are flying in.  In general it's commonly taught to pilots that you begin your descent from the traffic pattern to land when you are on the downwind leg and abeam the threshold of the runway you are going to land on.  You will select a descent power setting at this point, configure the aircraft for landing and begin the descent.  When you turn base or final is going to be up to your discretion but in general should be no more than 1-2 miles from the airport.  This turning point may also be given to you by ATC at a towered airport for aircraft spacing e.g. "Cessna 1 2 3 X-ray yankee, extend your downwind; I'll call your base."  You may also have to do the same thing at "beehives" or busy, non-towered airports for traffic spacing in the pattern as well.

Unless there is other traffic to follow or I am asked to extend my downwind, when I am beam the numbers I add the first notch of flaps and pull the power to begin a 500' per minute descent. Then begin slowing to final approach speed. (70 to 90 mph depending on airplane) If you do it like the book says, you'll fly a good pattern every time.

Note the OP's "helicopter" tag - does this affect the answer?


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Can you have TCAS RA if your other traffic only have TCAS TA?
If you fly and have a TCAS TA, it announce "TRAFFIC, TRAFFIC!"
However, the other traffic executed a TCAS RA and did the "UNKNOWN" manouvre.
Is it possible? As what i remember, it does takes two aircraft in RA mode. Unless you selected TA MODE ONLY.
Please give me reference about this.
Thank you

See also Can TCAS give an RA for one aircraft and a TA for another?

If both aircraft in an encounter are equipped with TCAS and are operating in TA/RA mode, then both will receive a coordinated RA.  That is the RA will be coordinated between them using the Mode S datalink.
If both aircraft in an encounter are equipped with TCAS and one is operating in TA/RA mode and the other in TA Only mode, the one operating in TA/RA will receive an uncoordinated RA and the other will receive a TA. In an uncoordinated RA, the TCAS will provide guidance based on the observed path of the aircraft, modifying the RA as necessary.
If one aircraft in an encounter is equipped with TCAS and operating in TA/RA mode and the other in does not have an operating TCAS, but does have a transponder, the one operating in TA/RA will receive an uncoordinated RA.
There's a good guide to TCAS available from the FAA web site.


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Irrational acrophobia-like anxiety caused by wave soaring
This will probably sound utterly bonkers to many and I feel very awkward coming out with this publicly - I'm a gliding instructor with 650 hours flying experience, and I'm scared of heights.
It's totally irrational, and it's not really height-specific. I'm completely fine thermal soaring under cumulus clouds of any cloudbase, or even wave soaring along the edges of clouds. But as soon as I either fly out into a blue gap, or start to climb above and "detach" from the cumulus tops, or start getting close to some kind of mid-level clouds, I experience intense acrophobia-like panic attack symptoms that seem to be triggered by the perception of excess height. Even more daft; getting "closed in" above clouds actually relieves these symptoms.
Outside of flying I am confirmedly acrophobic - I can get tense changing a light bulb. But in all other aspects of flying I'm of above average confidence; as an instructor I'm of the "let them screw up so they can see what wrong looks like and how to put it right" breed, I take willing students on detailed spin avoidance sorties where we explore all sorts of ways the glider will spin, I love aerobatics, fly cross country at every opportunity and am no stranger to field landings.
So far my coping strategy, especially with students, is to go long instead of up; make the "this is the best part of the wave" excuse and go cross country along the wave bars. This does extract some fun out of the situation but ultimately is a lame excuse - I'm avoiding telling them that I don't want to go any higher. More frustratingly, I'm actually not bad at and do enjoy some aspects of wave soaring.
I really want to break this; to be able to take my students as high as they like and the glider is equipped to go, and claim the last height badges, but even a gold height right now feels like it'd be a psychologically out of control, hellish nightmare. I've tried pushing my own comfort limits with it over the last couple of years, but so far it hasn't made things any better.
How can I overcome this? Is this even a known about thing or am I some kind of peculiar one-off?

You must have unbelievable self control to push through that kind of reaction and function safely, so in a way you are peculiar. I've been flying since the mid 70s and have never run into this sort of thing. Lots of pilots are afraid of heights, but not to that panic attack level and it's only a problem when they aren't enclosed. @Jpe61 is right. Go see a psychologist who can do desensitization/adaptation treatment.

Your best bet would be
cognitive behavioral therapy, and one thing worth trying might be exposure therapy in simulated environment, a simple pc sim with VR glasses migh be sufficient.
Te thing with acrophobia and flying is, that an aircraft seems to form a safe space for those having the condition; pilots having acrophobia is certainly not unheard of.
Your situation migh not be a typical case of acrophobia. It seems  reasonable to conclude that while you otherwise function normally when flying, proximity to clouds and certain other situations trigger the fear by giving you a "sensation of height" and/or a percieved risk of collision, even if the threatening object is a cloud.
It may also be that what ypu experience when flying is not acrophobia, but some other situational fear. You really should see a therapist to figure this out, phobias rarely can be overcome by oneself.
One more thing: it is not entirely correct to say that any kind of phobia irrational. They all are in some way echoes of our primary survival instincts, some more, some less obviously. Realizing this and coming into terms with the phobia, accepting it as a warning signal might mitigate the symptoms some. In any case, see a therapist, there's no shame in that, and you have nothing to lose.


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How is the center ILS used on the 747-400?
The aircraft has 3 ILS receivers, but only ILS L and R in the CDUs. How does the ILS C is put into action?

What is CDUS?..

@DeltaLima Plural of CDU, the user interface to the FMC.

Isn’t it only used to feed the center autopilot in automatic approaches with all three autopilots engaged?

I know there is a way to at least show the readings off of it (needles). Not sure about tuning it

When @Terry flys the -400 he can tune the ILS's to different frequencies, and fly them all, at the same time...

@Dave  That's only true because Terry is like Chuck Norris that way... the rest of us wouldn't be able to do that. But Terry (or Chuck Norris) could.